The present invention relates to a new and improved method and apparatus for the automatic suppression of weather echoes, referred to as clutter, which can disturbingly arise, apart from the flying target or body-Doppler signal, as further Doppler signals in a pulse Doppler-tracking radar apparatus containing quadrature channels, wherein there is regulated the frequency of the Doppler signals or the phase relationship between the Doppler signals and a reference signal derived from the transmitted signal.
If tracking radar must follow a moving target in a space filled with moving clutter, then there should not be suppressed the fixed target echoes, rather the clutter from the moving weather zone, i.e. the moving echoes of a certain radial velocity region. This suppression basically can be carried out if, firstly, the difference of the radial velocities of target echoes and clutter are sufficiently large, and secondly, if the velocity of the clutter can be determined. The first condition cannot be influenced by the radar, but however often is fulfilled in many applications.
A known method for suppressing clutter is predicated upon a single-sideband modulation of a phase reference signal. For the momentary optimum compensation value determination there is known, for instance, from Swiss Pat. No. 566,012 a method wherein there is determined the clutter velocity in an additional clutter measuring gate. Here, a number of discrete compensation frequency values are automatically sampled and there is selected the most suitable value in each case for compensation of the clutter at the tracking measuring gate. However, such method has been found to be disadvantageous because the measurement of the clutter velocity and the clutter compensation cannot be related to the same spatial volume, since the clutter measuring gate must be shifted in relation to the tracking measuring gate. Additionally, an arrangement according to this method functions relatively slowly, since it is not regulated, and therefore, needs to pass through a great many non-useful compensation values. Since the sign of the velocity of the clutter can only be determined by sampling or testing a set of different compensation values, there cannot be obtained any assiduousness.